1. Field of the Invention
The invention relates to the technical field of a steering control apparatus and steering control method for a vehicle provided with an electric power steering apparatus such as EPS (Electronic controlled Power Steering).
2. Description of the Related Art
Japanese Patent Application Publication No. 6-211142 (JP-A-6-211142), for example, proposes one type of electric power steering apparatus that takes the back electromotive force of an electric motor into account. The electric power steering apparatus described in JP-A-6-211142 (hereinafter referred to as the “related art”) enables good steering feel to be obtained by calculating the back electromotive force of the electric motor based on the detected rotation speed of the electric motor, and correcting the applied voltage of the electric motor based on that calculated back electromotive force.
Incidentally, Japanese Patent Application Publication No. 2007-118785 (JP-A-2007-118785), for example, also proposes technology for preventing the steering feel according to the driver from deteriorating by correcting a q-axis target current when performing field weakening control on an electric motor.
The driving voltage of the motor is affected by physical or electrical limitations on the motor side, the specifications (such as the rated value) of the power supply such as a battery, or the SOC (State Of Charge) of the power supply that can change on a case-by-case basis, and thus has a fixed or variable upper limit value. Therefore, even if the applied voltage (which is one form of the driving voltage in this case) is corrected simply taking the back electromotive force into account as it is in the related art, the applied voltage is limited by the upper limit value and therefore may not be able to cancel the back electromotive force.
In this case, the back electromotive force may exceed the applied voltage, such that the motor falls into a power generating state. As a result, the motor may fall into a so-called reverse assist state in which the assist direction of the motor reverses from the direction in which assist is originally required. That is, with the related art there is the technical drawback that a steering operation by the driver may be impeded when the driving voltage of the motor is limited by the upper limit value.